In a conventional art, when the equilibrium of an equilibrium reaction is not biased toward the product system, the reaction efficiency (equilibrium conversion) is improved by biasing the equilibrium toward the product system through reactive distillation. For example, "Chemical Engineering" Vol. 57, No. 1, pages 77-79 (1993) explains the reactive distillation by presenting specific examples.
In general, when performing a relatively complicated reaction composed of at least two steps of equilibrium reactions, reactive distillation is carried out separately for each of the equilibrium reactions. For example, an International Laid-Open Patent Publication, No. WO091/09832, discloses a method of preparing diphenyl carbonates from dimethyl carbonate and phenol through two steps of equilibrium reactions. In this method, one reactive distillation column (reactive distillation equipment) is used for each equilibrium reaction, and therefore two reactive distillation columns are used in total.
However, in this conventional method, during the reactive distillation of the first-step equilibrium reaction for forming methyl phenyl carbonate from dimethyl carbonate and phenol, dimethyl carbonate as a raw material and methanol as a product form an azeotrope. Therefore, the equilibrium is not biased toward the product system, and the equilibrium reaction does not proceeds smoothly. Consequently, carbonate esters are not prepared efficiently. In addition, since two reactive distillation columns are used for the preparation of diphenyl carbonate, a problem arises, i.e., the cost of equipment and utility increases.
Thus, the above-mentioned conventional reactive distillation columns are used only for a relatively simple reaction. In other words, they are not used for a relatively complicated reaction composed of at least two steps of equilibrium reactions. Namely, there is very few known reactive distillation columns which are applicable to consecutive multiple reactions. In such a situation, there is a demand for reactive distillation equipment and reactive distillation methods applicable to a relatively complicated reaction composed of at least two steps of equilibrium reactions.
In order to solve the above-mentioned conventional problem, it is an object of the present invention to provide reactive distillation equipment applicable to a relatively complicated reaction composed of at least two steps of equilibrium reactions, and reactive distillation methods capable of performing such a reaction efficiently.